The present invention relates in general to segmented, control flaps or rudder devices on various commercial and military marine craft, aircraft, missiles, and spacecraft. In hydrofoils, for example, leading fluid foils have multiple control flaps, hingedly engaged at their leading edges to foil trailing ends for rotation with respect to the foil for control purposes. Generally, two flaps centrally positioned with respect to the span are driven by hinge means. In each pair of flaps extending spanwise therefrom, the inner flap is a driver and the outer is a driven flap. The driver has a key extending into a keyway in the driven flap so that when the driver is rotated on the hinge, the driven is simultaneously rotated. In order to provide a snug fit of the key in the keyway and to protect the metal surfaces of the key and the keyway, an elastic liner is positioned in the keyway and is of a configuration to snugly receive the key and a hinge pin.
In the prior art the liners have typically been destroyed, usually piece by piece, and have become separated from the flap assembly. This has resulted in metal-on-metal structural damage to the flaps. Such damage has required costly repair and replacements. In addition there has been early fatigue failure, coupled with loss of flight control.
Hydrofoils employing segmented trailing edge flaps produce a cavitating flow at the end-to-end junction of the flaps. Because there are a multiple number of these flap-to-flap interfaces, the negative effects of the cavitating flow on performance are cumulative. For example, there may be 20 flaps, accompanied by 14 of such end-to-end junctures. Pressure bleed through the gaps between the flaps causes increased drag and also reduces the flap effectivity, which has adverse effects on ship flight controls, particularly in high sea states.